With the rapid development in radio communication technology, various types of services such as voice communication, video communication, data communication, instant messaging, viewing a movie, a web service, a game, and the like are being provided. Users of these services demand abilities to transmit a large amount of data quickly while maintaining high quality.
In order to obtain a high transmission speed, there has been an active research on technology that may improve the transmission speed by installing multiple antennas in a base station. With the communication technology using multiple antennas, a diversity gain may be obtained from a plurality of radio channels that are formed between the multiple antennas. Multiple antennas may be provided between the base station and a terminal.
Multi-user diversity technology is a communication scheme that may concentrate data transmission on only a limited number of terminals with an excellent radio channel environment between a base station and the terminals, from among a plurality of terminals that exist in a cell-coverage of the base station, so as to improve a data transmission rate.
Accordingly, researches are being pursued with respect to a multi-user Multiple-Input Multiple-Output (MIMO) technology by combining teachings from a multi-user diversity technology and a MIMO communication technology. According to the multi-user MIMO technology, a base station may transmit data to multiple users via multiple antennas. Thus, a multi-user gain and a multiple antenna gain may be obtained.
However, interference may occur between multiple users when using the multi-user MIMO technology, which in turn may reduce the data transmission rate.
In order to improve the data transmission rate, a beamforming scheme may be performed for only particular users. Where data is transmitted to the particular users according to the scheme, the interference between the multiple users may be reduced.
However, the scheme of performing beamforming for only the particular users may cause other difficulties. For example, where it is assumed that a total of four users exist and only two users are selected as a beamforming target, two beamforming vectors corresponding to the selected two users may be selected, and beamforming may be performed for the selected two users based on the selected two beamforming vectors. In this case, unselected beamforming vectors may be wasted and thus the multi-user gain may be reduced. Since only beamforming vectors corresponding to particular users that are selected from a plurality of beamforming vectors are used for beamforming, the unselected beamforming vectors may reduce the efficiency of the system.
Accordingly, there is a need for a MIMO communication system and method that increases a multi-user gain by applying unselected beamforming vectors for beamforming.